Potential from two charges

1. The problem statement, all variables and given/known data
A charge of -1.9 × 10-9 C is at the origin and a charge of 9.4 × 10-9 C is on the x-axis at x = 3 m. At what two locations on the x-axis (xpositive, xnegative) is the potential zero?
xpositive = m
Xpositive = .5m
v=kq/x + (k(5Q/3-x))to solve for this value,
.5

xnegative = m
I'm lost on the second part of the problem which we need to calculate the X negative
If someone could help me set this equation up I would be very appreciative :)